The difference is in the type of worms producing the yarn
and the types of leaves they eat.
Mulberry silk is obtained from Bombyx Mori feeding on
Mulberry leaves.
Tussar silk is obtained from Antherea Mylitta feeding on
Arjun and Asan leaves.
Muga silk is obtained from Antherea Assamensis feeding on
Som and Sualu leaves.
Eri silk is obtained from Cynthia Ricini feeding on Castor
Oil leaves.
The Eri silk is the only completely domesticated silkworm
other than Bombyx Mori.